Judges are more lenient toward a psychopath when given a neuro explanation for his condition

Last month, a prescient editorial in the New York Times warned that a greater understanding of the neural correlates of behaviour risks having a distorting effect on the criminal justice system. John Monterosso and Barry Schwartz highlighted their own research showing that people are far more forgiving of crimes with ostensibly neurobiological causes, compared with psychological causes – a worrying demonstration of what they called "naive dualism" given that "all psychological states are also biological ones."

Now a multi-disciplinary team of psychologist Lisa Aspinwall, legal scholar Teneille Brown and philosopher James Tabery, has surveyed nearly 200 state trial court judges in the U.S., showing how their decision making is swayed by a neurobiological explanation for psychopathy.

The judges read about a case, based loosely on real events, in which a robber brutally attacked a restaurant manager who refused to hand over any money. All judges were given evidence from the prosecution or defence that said the perpetrator had been diagnosed with psychopathy – an untreatable condition. Additionally, half of them were also presented with expert evidence from a neurobiologist about the causes of psychopathy, including genetic factors. The perpetrator had been tested and had low MAOA activity – a profile, the judges were told, previously associated with increased propensity for anti-social behaviour. The neurobiologist also explained how this genetic profile leads to brain abnormalities that impair the psychopath's ability to tell right from wrong.

Compared with what they estimated to be their usual sentencing for aggravated battery (9 years), overall the judges said they would give a higher sentence to the psychopathic perpetrator in the current case – 12.93 years. This shows the criminal's psychopathy was overall treated as an "aggravating factor", a sign of utilitarian thinking on the part of the judges, in the sense that he was highly likely to be violent in the future.

However, among the judges exposed to a neurobiological account of psychopathy, the diagnosis also had a "mitigating" effect on their decision-making. Judges in this condition sentenced the attacker to an average of 12.83 years compared with the 13.93 years given by judges who didn't receive the neurobiological information. Although the judges in receipt of the neurobiology didn't agree with the explicit suggestion that the attacker had compromised free will or moral responsibility, their open-ended explanations for their sentencing suggested otherwise. The neural evidence "makes possible an argument that psychopaths are, in a sense, morally 'disabled'," said one.

Aspinwall and her team described as a "double-edged sword" the way that psychopathy, accompanied by neurobiological explanation, can have both an aggravating and mitigating effect at once. Supporting this, judges who received the neurobiological testimony, and heard the psychopathic diagnosis from the defence counsel, tended to mention "weighing" or "balancing" factors over twice as often as judges in the other conditions. "Psychopathy may make the defendant less morally culpable, but it increases his future dangerousness to society," said one. "In my mind, these factors balance out …".

This new research adds to a growing literature showing how people seem to be particularly beguiled by neuroscientific evidence. Last year, for example, a study reported that people were more persuaded by brain-scan-based lie-detection evidence compared with more traditional lie-detection approaches. This study also isn't the first to examine the factors affecting the decision-making of judges. For instance, it was shown last year that hungry judges are less forgiving.

Further reading

Lisa G. Aspinwall, Teneille R. Brown, & James Tabery (2012). The Double-Edged Sword: Does Biomechanism Increase or Decrease Judges' Sentencing of Psychopaths? Science : 10.1126/science.1219569